Mo. Rev. Stat. § 145.009

Sections 145.011 to 145.995 shall become effective January 1, 1981, but it shall apply only with respect to decedents dying on or after January 1, 1981. The repeal of the provisions of chapter 145 shall become effective January 1, 1981, but it shall not affect any decedents dying before January 1, 1981, in any respect, including, but not limited to, the determination of tax, interest, penalties, procedures, and periods of limitations.